e species, P.
cembra and its allies, with the cone-tissues so completely
parenchymatous that the cones cannot release the seeds except by
disintegration. In both subsections there is a gradual evolution from a
wingless nut to one with an effective wing, adnate in one subsection,
adnate and articulate in the other. The different stages of this
evolution are so distinct that the Soft Pines are easily separated into
definite groups.

Among the Hard Pines a few species show characters that are peculiar to
the Soft Pines. These exceptional species form a subsection
(Parapinaster) by themselves.

With the remaining species, the majority of the Pines, the distinctions
that obtain among Soft Pines have disappeared. The dorsal umbo, the
articulate seed-wing, the persistent fascicle-sheath, the dorsal and
ventral stomata of the leaf and its serrate margins, the dentate walls
of the ray-tracheids have become fixed and constant. But a new form of
seed-wing appears, with a thickened blade, assuming such proportions in
P. Sabiniana and its two allies that these three constitute a distinct
group, remarkable also for the size of its cones.

Here also appear a new form of fruit, the oblique cone, and a new method
of dissemination, the serotinous cone. Associated with the latter are
the persistent cone and the multinodal spring-shoot. These characters do
not develop in such perfect sequence and regularity that they can be
employed for grouping the species without forcing some of them into
unnatural association. The oblique cone first appears sporadically here
and there and without obvious reason. The persistent cone, the first
stage of the serotinous cone, is equally sporadic in the earlier stages
of evolution. The same may be said of the multinodal shoot.

Nevertheless these characters show an obvious progression toward a
definite goal, where they are all united in a small group of species
remarkable for the form and texture of their cones, for a peculiar
seed-release and for the vigor and rapidity of their growth. It is
possible, with the assistance of other characters, to segregate these
species in three groups in which the affinities are respected and the
general trend of their evolution is preserved.

The first group, the Lariciones, contains species with large ray-pits,
cones dehiscent at maturity, and uninodal spring-shoots. They are, with
two exceptions, P. resinosa and P. tropicalis, Old World species.

The second group,